1. Field of the Invention
This invention relates to a liquid analysis system having improved optical characteristics.
2. Prior Art
The invention is concerned with automated quantitative analysis of the continuous flow type, and especially the optical characteristics of such analysis utilizing a colorimeter, densitometer or fluorometer. Skeggs et al U.S. Pat. No. 3,241,432; Rosin et al U.S. Pat. No. 3,345,910; Rachlis et al U.S. Pat. No. 3,583,817; and Bellinger et al U.S. Pat. No. 3,740,158 disclose method and apparatus which exemplify the prior art.
The Skeggs et al U.S. Pat. No. 3,241,432 describes automated quantitative analysis of a series of liquid samples seriatum, wherein neighboring samples flowing along a conduit are separated by an immiscible fluid segment which is preferably a gas segment. The samples are treated and after removal of the immiscible fluid segments are flowed through a colorimeter flowcell (FIG. 7), having a straight sight path extending through curved surfaces of the glass cell, for photometric analysis. However, the curved glass surfaces, end window, through which light is directed, while having good fluid flow characteristics for the sweeping away of any fine bubbles or debris, often failed to exhibit optimum optic qualities. For example, some light from the source thereof may be absorbed in the end walls or refracted therefrom, resulting in loss of light transmission.
The Rosin et al U.S. Pat. No. 3,345,910 discloses a flowcell having flat end windows in the sight path, tending to lessen the aforementioned refraction problem of the curved glass end windows of the Skeggs et al flowcell. However, this window configuration caused fluid and debris entrapment in proximity to the lower internal corners of such windows which, when caused to shift somewhat by pulsations in flow in the cell, resulted in optical noise as pointed out in the Rachlis et al U.S. Pat. No. 3,583,817. The last-mentioned patent discloses a flowcell end window which has a planar, internally inclined surface which avoided such entrapment in the cell. However, all of the above-discussed flowcells exhibited loss of light transmission along the sight path caused by refraction of light within the end windows into the tubular wall structure of the flowcell.
The Bellinger et al flowcell of U.S. Pat. No. 3,740,158 alleviated the last-mentioned optical problem. It discloses an interface of a flowcell end window and the tubular wall structure of the cell wherein the material of the window has a higher refractive index than the material of the wall structure, so that the end window constitutes a light pipe for increased light transmission into the liquid in the flowcell path or out of it, or both. In accordance with the Bellinger et al disclosure any immiscible fluid segments in the sample stream may be removed from the stream in the use of the flowcell just prior to introduction of the sample stream into the flowcell. However, it was pointed out that it is preferred that for the purpose of cleansing the cell, these immiscible fluid segments pass through the cell.
In the use of all the above-described flowcells, there has been a loss of transmission of light along the sight path within the cell and in which liquid is conveyed because the liquid failed to exhibit light-piping characteristics therein, that is, light reflectivity within the liquid or, more precisely, reflectivity within the liquid at the interface thereof with the tubular wall structure of the flowcell. The present invention deals with overcoming this problem.